A woman in her 60s was found to have screen detected invasive lobular breast carcinoma of the right breast and invasive ductal carcinoma, no special type, of the left breast.
Staging CT imaging prior to mastectomy showed a 12 cm pelvic mass which on initial impression was thought to be a fibroid uterus.
Associated postmenopausal bleeding led to pelvic ultrasound, hysteroscopy and biopsy.
The biopsy showed undifferentiated sarcoma, unclassifiable with immunohistochemistry.
Following discussion at a multidisciplinary team meeting it was felt that the uterine tumour was a separate primary malignancy rather than metastasis from the breast.
Hysterectomy and bilateral salpingo-oophorectomy was performed for both treatment purposes and to fully categorise the malignancy to guide further adjuvant therapy.
Histological examination of the resection specimen showed a partially necrotic tumour with a discrete outline located within and extending throughout the myometrium.
The tumour was composed of malignant spindle cells (figure 1A), with an intermittent component of pleomorphic cells with abundant eosinophilic cytoplasm.
Plentiful osteoclast-like giant cells were present (figure 1B).
Mitoses were numerous and structurally abnormal forms were common.
Neoplastic cells were surrounded by hyaline osteoid matrix and foci of coarse neoplastic woven bone (figure 1C).
Generous sampling of the tumour showed no admixed neoplastic epithelial elements, thus ruling out the more common carcinosarcoma (malignant mixed Müllerian tumour).
Tumour cells showed immunohistochemical expression for vimentin, smooth muscle actin (SMA), desmin (focally) and CD99.
Epithelial markers were not expressed.
The morphological and immunohistochemical appearances were in keeping with primary uterine osteoblastic variant of osteosarcoma.
Unfortunately, despite treatment, further CT imaging showed the development of multiple peritoneal and pulmonary deposits, confirmed on biopsy to be metastatic osteosarcoma.
The patient received palliative chemotherapy and died several months later.